I own a Modulus Alembic Blacknife six string, that I bought from Stars Guitars in the early 70s. I noticed that the Blacknife is not made anymore. Does anyone know why and how many were made and the approximate value?

Modulus is probably your best source for this information as it was their production, despite the Alembic printing on the headstock.  
 
If you find out, please do post your results here, as I'm sure there will be other parties interested in what you learn.